1. Field of the Invention
The present invention generally relates to a module type multiphase inverter such as a three-phase inverter which generates a multiphase alternating current from a direct current and controls the driving of a multiphase alternating current motor, for example, mounted on a vehicle.
2. Description of Related Art
The inventor of this specification has proposed a three-phase inverter having three half bridge modules in Published Japanese Patent First Publication No. H13-308263. In this publication, each module is formed in a card shape and has an upper arm element and a lower arm element corresponding to one of three phases. Each element is made of a semiconductor chip and has both a direct current (DC) terminal connected with a battery and an alternating current (AC) terminal connected with a motor. A three-phase inverter circuit is composed of the arm elements of the three modules.
In this inverter, the DC terminal of each element is made of an electrode plate which is exposed to the atmosphere to form one principal surface of the module on one side along a thickness direction of the module. The AC terminals of the upper and lower arm elements of each module are made of a common electrode plate which is exposed to the atmosphere to form the other principal surface of the module on the other side along the thickness direction. Therefore, the use of the common electrode plate can simplify the wiring arrangement. Further, because the electrode plates are placed on both surfaces of each card type module so as to be exposed to the atmosphere, heat generated in the module can be smoothly dissipated or radiated to the atmosphere through the plates. Accordingly, each module can have a both-surface cooling effect peculiar to the card type module.
However, in each module of the inverter, semiconductor chips of the upper arm element are disposed to be inverted to those of the lower arm element along the thickness direction. For example, each chip of the upper arm element has an emitter, a base and a collector in that order along the thickness direction, and each chip of the lower arm element has a collector, a base and an emitter in that order along the thickness direction. Therefore, packaging of the chips into the module is undesirably complicated.
To solve this problem, there is an idea that six arm elements of three phases are disposed together on a common substrate to pack the arm elements in full package in a card type module structure. However, in this inverter having the single card type module, because heat radiation from both principal surfaces of the module is required to obtain the both-surface cooling effect in the module, terminals of six or twelve chips (i.e., one or two chips for each arm element) are inevitably led out from side surfaces of the module, and wires for control signals and wires for power supply are extended toward the side surfaces of the module. Therefore, the leading of the terminals protruded from the side surfaces of the module and connection of the wires with the terminals are undesirably complicated. Further, because the wires are inevitably lengthened, surge noises caused by inductance of the wirings and power loss based on resistance of the wirings are undesirably increased.
Further, because all the arm elements are disposed on a single plate, this inverter inevitably has a large plane area. Therefore, when the inverter is packed into a motor of a vehicle, the installation of the motor in the vehicle is restricted. Moreover, the area of each principal surface of this module is increased, and size and weight of cooling members attached to the principal surfaces of the module are undesirable increased.